Computer modelling of strength and vibrations of steam turbine elements
Abstract
The objective of this study is to develop an effective method for analyzing the strength and vibrations of steam turbine components.
Relevance
In modern circumstances, the need to replace or upgrade equipment that has been in operation for extended periods has become increasingly critical. The rising demands for enhanced reliability and efficiency of power plants have made the modernization of hydroturbine and steam turbine systems at hydroelectric facilities a pressing priority. The situation with power equipment has become particularly challenging in the context of ongoing hostilities. During operation, the blades of hydraulic and steam turbines are exposed to significant loads from the working medium (fluid) they interact with, resulting in forced oscillations. If the natural frequencies of these oscillations align with the frequencies of external forces, resonance can occur, potentially causing severe damage or even complete equipment failure. This underscores the importance and timeliness of this study, which seeks to address these critical issues and enhance the performance and reliability of turbine equipment.
Research methods
To solve the problem of modelling the strength and vibrations of steam turbine elements, the methods of given modes as well as finite and boundary element methods were used
The results
Both continuous and discrete mathematical models were created to assess stresses and deformations in elastic elements of structures and to determine the frequencies and modes of their free oscillations. The discrete mathematical model employs finite and boundary element methods. Using the finite element method, the static characteristics and free oscillation modes of blades in air are calculated. The boundary element method is used to determine the matrix of attached fluid masses, assuming the fluid is incompressible, ideal, and its motion induced by the blade oscillations is vortex-free. The fluid pressure problem is simplified to a hypersingular integral equation, for which an effective numerical solution method is proposed. The method is relied on analytical formulae for calculating both singular and hypersingular parts. Additionally, the stress-strain state and deflections of the blade under aerodynamic, weight, and inertial loads are determined. Areas of maximum stress are identified, and recommendations for improving the geometric parameters of the model and the potential use of materials with enhanced properties are provided.
Conclusions
The mathematical model has been developed to analyze the static and dynamic characteristics of hydraulic and steam turbine components. To create a discrete model suitable for numerical simulations, the finite element and boundary element methods were employed. The static state of the blade in the second crown of the final stage of a CNT steam turbine, operating at a capacity of over 1000 MW and a speed of 1500 rpm, has been thoroughly investigated. Zones of maximum stress were identified, providing critical insights into the structural performance. Based on the findings, recommendations have been proposed to optimize the geometric parameters of the blade and explore the potential application of materials with enhanced properties. Future work will involve conducting a detailed modal analysis to evaluate the vibrational characteristics of the blade, both with and without considering the attached fluid masses, to gain deeper insights into its dynamic behavior.
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References
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Sierikova O., Strelnikova E., Gnitko V. and Degtyarev K.: Boundary Calculation Models for Elastic Properties Clarification of Three-dimensional Nanocomposites Based on the Combination of Finite and Boundary Element Methods, 2021 IEEE 2nd KhPI Week on Advanced Technology (KhPIWeek), Kharkiv, Ukraine, pp. 351-356 (2021), https://doi.org/ 10.1109/KhPIWeek53812.2021.9570086
Avramov, K.V., and E.A. Strel'nikova. "Chaotic oscillations of plates interacting on both sides with a fluid flow." International Applied Mechanics, vol. 50, no. 3, 2014, pp. 329-335.
Sriti, M.: Improved blade element momentum theory (BEM) for predicting the aerodynamic performances of horizontal Axis wind turbine blade (HAWT), Technische Mechanik, 38, pp. 191–202, 2018, DOI: 10.24352/UB.OVGU-2018-028.
Gnitko V., Karaiev A., Degtyariov K., Strelnikova E. Singular boundary method in a free vibration analysis of compound liquid-filled shells, WIT Transactions on Engineering Sciences, vol.126, pp.189-200, 2019. WIT Press, https://doi.org/10.2495/BE420171.
Gnitko, V., Martynenko, O., Vierushkin, I., Kononenko, Y., Degtyarev, K. (2023). Coupled Finite and Boundary Element Methods in Fluid-Structure Interaction Problems for Power Machine Units. In: Altenbach, H., et al. Advances in Mechanical and Power Engineering. CAMPE 2021. Lecture Notes in Mechanical Engineering. Springer, Cham. https://doi.org/10.1007/978-3-031-18487-1_29
